1. Field of the Invention
The present invention is directed to receivers and, more particularly, to digital signal processing (“DSP”) based receivers, electrical receivers, optical receivers, parallel receivers, multi-channel receivers, timing recovery schemes, and without limitation, equalization schemes.
2. Related Art
There is an ever-increasing need for higher speed communications systems. In order to reduce costs, communications systems are increasingly implemented using Very Large Scale Integration (VLSI) techniques. The level of integration of communications systems is constantly increasing to take advantage of advances in integrated circuit manufacturing technology and the resulting cost reductions. This means that communications systems of higher and higher complexity are being implemented in a smaller and smaller number of integrated circuits. For reasons of cost and density of integration, the preferred technology is CMOS.
Digital Signal Processing (“DSP”) techniques generally allow higher levels of complexity and easier scaling to finer geometry technologies than analog techniques, as well as superior testability and manufacturability. However, DSP based communications systems require for their implementation an analog-to-digital converter (“ADC”). In many applications, the ADC is challenging to design. In the extreme, the ADC requirements sometimes limit the practicality of building DSP-based communications systems. One such case occurs when the speed of the communication system is very high, for example in the gigabit per second range.
There is growing demand for communications systems that operate at data rates in the gigabit per second range. Examples of such systems are transceivers for optical communications for standards such as OC-48, OC-192, and OC-768, 10 gigabit Ethernet, Fibre Channel, etc. Another example is a transmission system where the communication channel is a micro-strip delay line on a printed circuit (“PC”) board. These communications systems typically operate over short distances and they are used to interconnect chips on a PC board or on different PC boards across a back plane in a rack-based system. These systems typically operate at data rates of several gigabits per second, and there is a need to increase the speed to the limits allowed by the technology. Additional examples could be found in transmission systems operating over short lengths of coaxial, twisted pair, or twin-ax cable.
Data signals are affected by various types of impairments, such as intersymbol interference. These impairments get progressively worse at higher data rates. Therefore, there is a need for methods and systems for compensate for intersymbol interference, to facilitate higher rate of data transmissions.